This invention concerns an apparatus for processing data, and in particular a multi-staged indicator for use as a strain gauge load cell indicator. The apparatus may be especially adapted for monitoring loads in the mechanical workings of a torque arm reducer.
Data from mechanical systems frequently concerns very low frequency information, i.e., below several Hertz, mixed in with much higher frequency transient signals and rapid overloads. Also, sudden polarity changes are not unusual, even at high signal level values.
Accurate monitoring of loads in mechanical systems requires an indicator having special characteristics and qualities to accomodate such data. In general, prior art indicator systems do not effectively exhibit such special attributes. Many prior art indicator systems act too fast to provide a stable indication of load values under fluctuating value and polarity load conditions. Limit detectors of such prior art devices which are too fast acting provide nuisance trip outs under even minor conditions of overload, and hence do not satisfactorily perform their assigned function.
In general, prior art devices simply do not effectively handle alternating (+) and (-) load polarities. In mechanical systems, such as those associated with torque arm reducers, alternating polarity changes in monitored loads are indicative of alternating compression and tension in the respective mechanical element which is being monitored. Therefore, the many vibrations which may occur typically in a mechanical system are manifested in detection signals as signal polarity changes.
In general, prior art indicator devices and systems which attempt to monitor such alternating compression and tension effectively in mechanical systems with conventional indicator devices usually fail. For example, failing conventional devices might inefficiently cause the indicated signal level to sweep through zero, as would a mechanical meter arm, to indicate a polarity change. Failure of such prior art devices may result from the above-mentioned problem that steady state mechanical data is of a relatively low frequency while the alternating polarity changes and transient signals which may accompany such mechanical data can be of relatively high frequency. The present invention is intended to recognize and overcome such problems and failures as associated with some prior art devices.
Prior art indicator devices also have other shortcomings which may lessen effective monitoring of mechanical load system data. For example, not only are limit detectors of conventional devices generally too fast acting to provide desirable trip out performance, but they frequently lack any convenient means for setting and reading out associated limit set points.
Normally, because conventional indicator devices do not generally utilize the staged data processing approach of the present invention, they cannot readily provide a high frequency monitor output for conveniently and accurately tracking dynamic and transient operating load information. Such information may occur simultaneous with and be mixed in with steady state load information, as discussed above. This invention can provide such a high frequency monitor level output by virtue of a multi-staged data processing feature.
One example of a conventional indicator system is the Newport Q2000X digital indicator/controller, produced by the Newport Electronics Corporation of Santa Ana, Calif. The Q2000X is a modular-type system digital indicator/controller. It has a plurality of motherboards, analog outputs, control outputs, signal conditioner inputs and the like from which to choose. Signal conditioner inputs C and S of the Q2000X system are, respectively, AC average voltage and strain-gauge inputs. These two options are mutually exclusive in the Newport digital indicator system.
Option C, the AC average voltage signal conditioner input, has a rated input range of 47 through 1000 Hertz. However, 47 Hertz is generally too high of a frequency to include raw steady-state and low frequency transient data from a mechanical load system, which inclusion is one specific concern of this invention.
Option S, the strain gauge input of the Newport system, has a two Hertz low pass two-pole active filter. However, again this is a relatively high cut-off frequency for steady-state mechanical data and generally tend to give fluctuating or unstable digital readings.
A further drawback of the Newport Q2000X system when applied to a mechanical data environment is that its analog output is also limited to two Hertz. An analog output frequency limited to two Hertz is too low of a cut-off frequency to give valid data for any dynamic or transient mechanical analysis.
Additional features of conventional systems, as exemplified by the Newport system, present other problems which are addressed and overcome by this invention. For example, the Newport system has a latchable alarm, but it generally does not lock onto a reading of the data value at the time of alarm activation for subsequent display. Furthermore, the RMS-DC input option of the Newport system does not have any type of polarity sign detector. Similarly, that same input option does not have any peak/average control of system time constants. Also, the alarm system of Newport is not an integrating type, and thus does not specifically reduce the number of nuisance trip outs. The typical conventional system as exemplified by Newport generally lacks such further features as limit by-pass, built-in resistor calibration for the sensor and optional trailing display selection.
Some other prior art also has inherent drawbacks, but differs from the Newport System. For example, the U.S. Pat. No. 4,310,060to Phillips, Jr. et al. discloses an apparatus for monitoring the blending of fibers by measuring with load cells the weight of fibers in a pan. An analog signal from a load cell is converted to a digital signal and then processed in a subtractor and a latch circuit. The latch circuit is triggered whenever the weigh pan is found to be full. A chart recorder records the filling cycle for the weigh pan, and an associated alarm is actuated if indicated weights fall outside permitted tolerances.
Another weighing system disclosed by Wise (U.S. Pat. No. 3,918,539) monitors weight signals to control the rate of feeding of material onto a weigh pan. The detected load cells may comprise either a strain gauge disposed so as to support the weigh pan, or a device for detecting the movement of an arm attached to a weigh pan.